Methods of manufacturing large-area sputtering targets using interlocking joints

ABSTRACT

In various embodiments, joined sputtering targets are formed at least in part by spray deposition of the sputtering material and/or welding.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/628,090, filed Sep. 27, 2012, which claims the benefit of andpriority to U.S. Provisional Patent Application No. 61/540,644, filedSep. 29, 2011, and U.S. Provisional Patent Application No. 61/648,333,filed May 17, 2012, the entire disclosure of each of which is herebyincorporated herein by reference.

TECHNICAL FIELD

In various embodiments, the present invention relates to methods offorming large sputtering targets, in particular by joining smallersputtering-target tiles.

BACKGROUND

Sputtering, a physical-vapor-deposition technique, is utilized in manyindustries to deposit thin films of various materials with highlycontrollable composition and uniformity on any of a variety ofsubstrates. However, for many applications, the size of the desiredsubstrate continues to increase, necessitating the use of larger andlarger sputtering targets during the sputtering process. Unfortunately,sputtering targets formed via conventional fabrication methods tends tobe too small for many such applications, particularly if thesputtering-target material is a composite (i.e., a substantially uniformmixture of two or more elemental or compound components), as suchcomposite sputtering targets are difficult or impossible to form with ahigh degree of uniformity by other methods such as rolling. For example,alloys or mixtures of molybdenum and titanium (Mo/Ti) are typicallyformed into billets for sputtering targets via hot isostatic pressing(HIP) of a mixture of Mo and Ti powders. The largest such billets tendto be smaller than the sputtering-target size desired for, e.g.,sputtering of Mo/Ti films on large glass substrates for flat paneldisplays (FPDs). In order to provide sputtering targets of the requisitedimensions, multiple smaller targets are often positioned in closeproximity to each other (but not otherwise joined together) to form alarger target. For example, for use in a “generation 7” sputtering tool,12 planar plates having dimensions 2700 mm×200 mm×18 mm may be used toform a larger segmented target of approximate dimensions 2700 mm×2400mm×18 mm.

Such segmented targets present many disadvantages in terms of particlegeneration (which results in expensive yield loss for the manufacturer)and film nonuniformity. Particle generation may occur preferentiallyalong the edges of the individual sub-targets, and film uniformity tendsto decrease as the edges of the target are approached and/or as theedges of the sub-targets are exposed to the sputtering process. Particlegeneration is a particular problem for FPDs, as each particle generatedduring the thin-film deposition process can cause a pixel to fail, whichin turn has a deleterious impact on image quality and sharpness in thefinished FPD.

Similarly, tubular (or “rotary”) sputtering targets are frequently of asegmented design simply because some sputtering materials (e.g.,tantalum (Ta) or composites such as Mo/Ti), generally cannot be formedin sufficiently long tubes. For example, in order to make a long rotarytarget, multiple short cylindrical tiles of the sputtering material areoften simply slipped over and bonded to a tubular backing plate madefrom an easily formable material such as stainless steel or Ti. A single2.7-meter tube may have six or more tiles, the edges (as many as 12) ofwhich potentially generate contaminating particles. Particle generationis exacerbated in rotary sputtering machines, because such machinestypically contain multiple tubular targets. For example, a “generation8.5” sputtering tool typically contains 12 separate rotary targets, andthus 144 tile edges potentially generating particles.

Techniques such as electron-beam welding have been utilized in attemptsto join sub-targets together to form a larger sputtering target, e.g., acomposite target of a material such as Mo/Ti. However, electron-beamwelding of Mo/Ti sputtering-target sections results in unacceptableporosity in the welded zone due to the relatively high gas (e.g.,oxygen) content of the Mo and Ti in the plates. Furthermore, theelectron-beam-welded zone tends to have a markedly differentmicrostructure than that of the bulk of the target, which generallyresults in deleterious nonuniformity in films sputtered from such joinedtargets.

In view of the foregoing, there is a need for methods of joining smallersputtering targets to form large joined targets with joints that aremechanically robust and that do not generate particles during sputteringof the joined target.

SUMMARY

In accordance with various embodiments of the present invention, largesputtering targets are formed by tiling together multiple smallersputtering targets (or “tiles”) each having a desired composition andjoining the tiles at least partially by spray deposition (e.g., coldspray) and/or welding techniques. The present embodiments areparticularly applicable to sputtering targets including or consistingessentially of composite materials or alloys such as Mo/Ti,tungsten/titanium (W/Ti), or copper/tungsten (Cu/W), and are alsoapplicable to targets of a single material such as Ti, niobium (Nb), Ta,etc. The tiles may be, at least initially, shaped as rectangular prismsor cylinders with substantially right-angled corners. However, the tilesare generally not merely placed in close proximity and spray-coated atthe seams therebetween, as such joints may have insufficient strength towithstand subsequent handling and processing. Rather, a shaped jointarea is formed in at least one of the tiles at each interface or seambetween tiles, and this joint area is at least partially filled and/orcoated via spray deposition to form the joint. Such joints mayadvantageously have superior strength, resistance to particle formation,and microstructures and densities substantially resembling those of thejoined plates. The spray-deposited portion of the joint enables theelimination of internal exposed “edges” in the larger joined targets.Such joined targets may have areal dimensions of at least 2800 mm×2500mm (if planar), or even larger. Rotary joined targets in accordance withembodiments of the invention have lengths of 2.7 meters or even longer.However, joined sputtering targets having smaller areal dimensions orshorter lengths may also be produced in accordance to the embodiments ofthe invention. Typically the sputtering targets include or consistessentially of only the desired material to be sputtered, and afterjoining, the joined target is bonded to a backing plate, although insome embodiments the joining of the targets is performed directly on abacking plate. As used herein, a “backing plate” may be substantiallyplanar, tubular, or cylindrical, depending on the geometry of the finaldesired sputtering target, and may include or consist essentially of oneor more materials having a melting point less than that of the targetmaterial and/or less than the temperature of the spray material duringspray deposition. Herein, references to the joining of twosputtering-target tiles (thereby forming an interface therebetween) areunderstood to include cases where more than two tiles are joinedtogether at the same interface or at multiple different interfaces (andthus are not limited to cases in which only two tiles are joined), assuch cases include the joining of various combinations of two differenttiles.

The tiles to be joined may be fabricated with any one or more of avariety of techniques, including HIP, cold isostatic pressing (CIP),spray deposition, molding, etc. As mentioned above, the tiles may, atleast initially, have rectangular prismatic or cylindrical shapes withsubstantially right-angled corners, and then shaped joints (e.g., bevelsor chamfers) may be machined or otherwise introduced into the tilesprior to joining them together. Alternatively, the tiles may beinitially shaped already incorporating the bevel (or other suitableshape for joining) via a process such as molding in a shaped mold.

In an aspect, embodiments of the invention feature a method of forming ajoined sputtering target that includes or consists essentially of asputtering material. Two discrete sputtering-target tiles, which includeor consist essentially of the sputtering material, are disposedproximate each other to form an interface between the tiles. Theinterface includes a gap between the tiles. At least a portion of thegap is filled with a gap-fill material. A spray material isspray-deposited on at least a portion of the gap-fill material (as wellas, e.g., a portion of one or both tiles) to form a partial joint. Afterformation of the partial joint, at least a portion of the gap-fillmaterial is removed from the interface. After such removal, additionalspray material is spray-deposited on at least a portion of the partialjoint to join the tiles and form the joined sputtering target.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. Filling the at least a portion of thegap with the gap-fill material may alter the microstructure of at leastone of the tiles in a region proximate the interface. At least a portionof the altered-microstructure region may be removed prior tospray-depositing the spray material on at least a portion of the partialjoint. The gap-fill material may include or consist essentially of aweld bead and/or a rod (which may be hollow) shaped to (and/ordeformable to) fill at least a portion of the gap. The sputteringmaterial may include or consist essentially of a mixture or alloy of atleast two constituent materials. The gap-fill material may include orconsist essentially of at least one (e.g., only one) of the constituentmaterials. The constituent materials may include or consist essentiallyof Mo and Ti. The spray material may include or consist essentially ofat least one of (e.g., only one) of the constituent materials. The spraymaterial may include or consist essentially of the sputtering material.The tiles may consist essentially of the sputtering material. Thegap-fill material may include or consist essentially of the sputteringmaterial. At least a portion of each of the two tiles may besubstantially planar (and the joined target may be substantiallyplanar). At least a portion of each of the two tiles may besubstantially tubular (and the joined target may be substantiallytubular).

The interface may include at least one recess defined by a beveledsurface of at least one of the two tiles. The spray material maysubstantially fill the at least one recess to form a surfacesubstantially coplanar with a surface of at least one of the tiles. Thebeveled surface may be reentrant. At least a portion of the beveledsurface may be substantially planar and form an angle of greater than45° with respect to the normal to the top surface of the joinedsputtering target. The angle may be selected from the range of 45° to60°. Spray material may be spray deposited on the gap-fill material oron the partial joint at an angle approximately perpendicular to thebeveled surface. Spray material may be spray deposited on the gap-fillmaterial or on the partial joint by (i) spray-depositing a first portionof the spray material at an angle approximately perpendicular to thebeveled surface and (ii) thereafter, spray-depositing a second portionof the spray material at an angle approximately perpendicular to the topsurface of the joined sputtering target. After its formation, the joinedsputtering target may be annealed at a temperature selected from therange of approximately 480° C. to approximately 1425° C., or at atemperature selected from the range of approximately 1100° C. toapproximately 1425° C. The joined sputtering target may be disposed on abacking plate after formation of the joined sputtering target. Thejoined sputtering target may be heat treated at least proximate thespray material. The spray material may be spray-deposited on thegap-fill material and/or on the partial joint by cold spray.

In another aspect, embodiments of the invention feature a method offorming a joined sputtering target that includes or consists essentiallyof a sputtering material. A mechanical joint is formed between twodiscrete sputtering-target tiles by overlapping and/or interlocking thetiles at an interface therebetween. The interface includes a recess overthe mechanical joint. The tiles are joined by welding the mechanicaljoint. Thereafter, a spray material is spray-deposited over at least aportion of the welded mechanical joint to substantially fill at least aportion of the recess, thereby forming the joined sputtering target.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. Welding the mechanical joint mayinclude or consist essentially of resistance seam welding. Thesputtering material may include or consist essentially of a mixture oralloy of at least two constituent materials. Welding the mechanicaljoint may include or consist essentially of melting at least oneconstituent material while at least one other constituent materialremains unmelted. The constituent materials may include or consistessentially of Mo and Ti. The spray material may include or consistessentially of at least one of (e.g., only one) of the constituentmaterials. The spray material may include or consist essentially of thesputtering material. The tiles may consist essentially of the sputteringmaterial. The mechanical joint may include or consist essentially of aninterlocking joint that includes or consists essentially of atongue-in-groove joint, a dovetail joint, a rabbet joint, a fingerjoint, or a spline joint. At least a portion of each of the two tilesmay be substantially planar (and the joined target may be substantiallyplanar). At least a portion of each of the two tiles may besubstantially tubular (and the joined target may be substantiallytubular).

The recess may be defined by a beveled surface of at least one of thetwo tiles. The beveled surface may be reentrant. At least a portion ofthe beveled surface may be substantially planar and form an angle ofgreater than 45° with respect to the normal to the top surface of thejoined sputtering target. The angle may be selected from the range of45° to 60°. Spray material may be spray deposited at an angleapproximately perpendicular to the beveled surface. Spray material maybe spray deposited by (i) spray-depositing a first portion of the spraymaterial at an angle approximately perpendicular to the beveled surfaceand (ii) thereafter, spray-depositing a second portion of the spraymaterial at an angle approximately perpendicular to the top surface ofthe joined sputtering target. After its formation, the joined sputteringtarget may be annealed at a temperature selected from the range ofapproximately 480° C. to approximately 1425° C., or at a temperatureselected from the range of approximately 1100° C. to approximately 1425°C. The joined sputtering target may be disposed on a backing plate afterformation of the joined sputtering target. The joined sputtering targetmay be heat treated at least proximate the spray material. The spraymaterial may be spray-deposited by cold spray.

In yet another aspect, embodiments of the invention feature a method offorming a joined sputtering target that includes or consists essentiallyof a sputtering material. Two discrete sputtering-target tiles aredisposed substantially in contact at an interface therebetween. A firstwelding electrode is disposed above the interface, and a second weldingelectrode is disposed below the interface. The first welding electrodeis translated along at least portions of top surfaces of the tiles alongthe interface while, simultaneously, the second welding electrode istranslated along at least portions of bottom surfaces of the tiles alongthe interface. The first welding electrode remains disposedsubstantially above the second welding electrode as the electrodes aretranslated. During at least part of the translation of the first andsecond welding electrodes, an electrical current is passed through thetiles between the first and second welding electrodes to weld the tilestogether at the interface, thereby forming the joined sputtering target.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. A spray material may bespray-deposited on at least a portion of at least one of the tiles priorto disposing the tiles substantially in contact. The spray material maybe disposed at the interface after the tiles are disposed substantiallyin contact. The spray material may include or consist essentially of thesputtering material. The sputtering material may include or consistessentially of a mixture or alloy of at least two constituent materials.The spray material may include or consist essentially of at least one of(e.g., only one) of the constituent materials. Spray-depositing thespray material may include or consist essentially of cold spray. Weldingthe tiles together may include or consist essentially of melting atleast one constituent material while at least one other constituentmaterial remains unmelted. The constituent materials may include orconsist essentially of Mo and Ti. The tiles may consist essentially ofthe sputtering material. Mechanical force may be applied to theinterface with the first and second welding electrodes. At least aportion of each of the two tiles may be substantially planar (and thejoined target may be substantially planar). At least a portion of eachof the two tiles may be substantially tubular (and the joined target maybe substantially tubular). After its formation, the joined sputteringtarget may be annealed at a temperature selected from the range ofapproximately 480° C. to approximately 1425° C., or at a temperatureselected from the range of approximately 1100° C. to approximately 1425°C. The joined sputtering target may be disposed on a backing plate afterformation of the joined sputtering target. The joined sputtering targetmay be heat treated at least proximate the interface. The interface maydefine a plane that is not perpendicular to the top and/or bottomsurfaces of the tiles.

In another aspect, embodiments of the invention feature a joinedsputtering target comprising a sputtering material that comprises analloy or mixture of first and second constituent materials. The joinedsputtering target includes or consists essentially of first and seconddiscrete sputtering-target tiles joined at an interface therebetween,the first and second tiles each including or consisting essentially ofthe sputtering material. Across the interface, (i) regions of the firsttile consisting essentially of the first constituent material are bondedto regions of the second tile consisting essentially of the firstconstituent material, (ii) regions of the first tile consistingessentially of the first constituent material are bonded to regions ofthe second tile consisting essentially of the second constituentmaterial, (iii) regions of the first tile consisting essentially of thesecond constituent material are bonded to regions of the second tileconsisting essentially of the first constituent material, and (iv)regions of the first tile consisting essentially of the secondconstituent material are not bonded to regions of the second tileconsisting essentially of the second constituent material.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The bonded regions may be partiallymelted and/or partially interdiffused. The first constituent materialmay include or consist essentially of Ti and the second constituentmaterial may include or consist essentially of Mo. The first and secondtiles may each consist essentially of the sputtering material.

In a further aspect, embodiments of the invention feature a method offorming a joined sputtering target including or consisting essentiallyof a sputtering material. Two discrete sputtering-target tiles, whichinclude or consist essentially of the sputtering material, are disposedproximate each other, thereby forming an interface between the tiles.The interface includes or consists essentially of an interlocking jointtherein and/or a recess in a top surface thereof. A spray material isspray-deposited over at least a portion of the interface, therebyjoining the tiles to form the joined sputtering target.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. Disposing the two tiles proximate eachother may include or consist essentially of disposing the two tilessubstantially in contact with each other. At least a portion of each ofthe two tiles may be substantially planar (and the joined target may besubstantially planar). At least a portion of each of the two tiles maybe substantially tubular (and the joined target may be substantiallytubular). The spray material may include or consist essentially of thesputtering material. The tiles may consist essentially of the sputteringmaterial. The sputtering material may include or consist essentially ofa mixture or alloy of at least two constituent materials. Theconstituent materials may include or consist essentially of Mo and Ti.The spray material may include or consist essentially of at least one of(e.g., only one) of the constituent materials. The interface may includea recess, and the spray deposition may fill at least a portion of therecess with the spray material. The interface may include a recessdefined by a beveled surface (which may be reentrant) of at least one ofthe two tiles.

At least a portion of the beveled surface may be substantially planarand form an angle of greater than 45° with respect to the normal to thetop surface of the joined sputtering target. The angle may be selectedfrom the range of 45° to 60°. Spray material may be spray deposited atan angle approximately perpendicular to the beveled surface. Spraymaterial may be spray deposited by (i) spray-depositing a first portionof the spray material at an angle approximately perpendicular to thebeveled surface and (ii) thereafter, spray-depositing a second portionof the spray material at an angle approximately perpendicular to the topsurface of the joined sputtering target. After its formation, the joinedsputtering target may be annealed at a temperature selected from therange of approximately 480° C. to approximately 1425° C., or at atemperature selected from the range of approximately 1100° C. toapproximately 1425° C. The interface may include an interlocking jointthat includes or consists essentially of a tongue-in-groove joint, adovetail joint, a rabbet joint, a finger joint, or a spline joint. Anedge of at least one of the tiles may be beveled prior to disposing thetiles proximate each other, and the beveled edge(s) may form at least aportion of the recess. Spray-depositing the spray material may includeor consist essentially of cold spray. The joined sputtering target maybe sputtered, and the spray-deposited material may substantially preventparticle generation at the interface. The joined sputtering target maybe disposed on a backing plate after spray deposition. The two tiles maybe disposed proximate each other on a backing plate prior to spraydeposition. The joined sputtering target may be heat treated at leastproximate the spray material. The interface may define a plane that isnot perpendicular to the top and/or bottom surfaces of the joinedsputtering target.

In yet a further aspect, embodiments of the invention feature a joinedsputtering target including or consisting essentially of a sputteringmaterial. The joined sputtering target includes or consists essentiallyof two discrete sputtering-target tiles joined at an interfacetherebetween. The tiles include or consist essentially of the sputteringmaterial. The interface includes a recess therealong at least partiallyfilled with unmelted powder.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The two tiles may be joined atopposing edges, and the interface may include portions of the twoopposing edges substantially in contact with each other and disposedbeneath the at least partially filled recess. One of the two opposingedges may at least partially (or even completely) overlap the otheropposing edge at the interface below the at least partially filledrecess. The interface may define a plane that is not perpendicular tothe top and/or bottom surfaces of the joined sputtering target. Aninterlocking joint that includes or consists essentially of portions ofthe two tiles may be present at the interface. The interlocking jointmay include or consist essentially of a tongue-in-groove joint, adovetail joint, a rabbet joint, a finger joint, or a spline joint. Atleast one of the tiles may include a beveled edge, and the bevelededge(s) may form at least a portion of the recess. The at least onebeveled edge may have a reentrant surface. At least a portion of the atleast one beveled edge may be substantially planar and form an angle ofgreater than 45° with respect to the normal to the top surface of thejoined sputtering target. The angle may be selected from the range of45° to 60°.

The unmelted powder may include or consist essentially of the sputteringmaterial. The tiles may consist essentially of the sputtering material.The sputtering material may include or consist essentially of a mixtureor an alloy of at least two constituent materials. The unmelted powdermay include discrete regions each substantially free of at least one ofthe constituent materials. The joined sputtering target may include atleast one region at the interface in which at least two of theconstituent materials are interdiffused. The constituent materials mayinclude or consist essentially of Mo and Ti. A backing plate may beattached to the tiles. The unmelted powder may be in contact with thebacking plate. At least a portion of the joined sputtering target may besubstantially planar. At least a portion of the joined sputtering targetmay be substantially tubular.

In another aspect, embodiments of the invention feature a joinedsputtering target including or consisting essentially of a sputteringmaterial. The joined sputtering target includes or consists essentiallyof two discrete sputtering-target tiles joined at an interfacetherebetween. The tiles include or consist essentially of the sputteringmaterial. The interface includes a recess therealong at least partiallyfilled with melted powder.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The two tiles may be joined atopposing edges, and the interface may include portions of the twoopposing edges substantially in contact with each other and disposedbeneath the at least partially filled recess. One of the two opposingedges may at least partially (or even completely) overlap the otheropposing edge at the interface below the at least partially filledrecess. The interface may define a plane that is not perpendicular tothe top and/or bottom surfaces of the joined sputtering target. Aninterlocking joint that includes or consists essentially of portions ofthe two tiles may be present at the interface. The interlocking jointmay include or consist essentially of a tongue-in-groove joint, adovetail joint, a rabbet joint, a finger joint, or a spline joint. Atleast one of the tiles may include a beveled edge, and the bevelededge(s) may form at least a portion of the recess. The at least onebeveled edge may have a reentrant surface. At least a portion of the atleast one beveled edge may be substantially planar and form an angle ofgreater than 45° with respect to the normal to the top surface of thejoined sputtering target. The angle may be selected from the range of45° to 60°.

The melted powder may include or consist essentially of the sputteringmaterial, and may have been deposited via thermal spray. The tiles mayconsist essentially of the sputtering material. The sputtering materialmay include or consist essentially of a mixture or an alloy of at leasttwo constituent materials. The melted powder may include discreteregions each substantially free of at least one of the constituentmaterials. The joined sputtering target may include at least one regionat the interface in which at least two of the constituent materials areinterdiffused. The constituent materials may include or consistessentially of Mo and Ti. A backing plate may be attached to the tiles.The melted powder may be in contact with the backing plate. At least aportion of the joined sputtering target may be substantially planar. Atleast a portion of the joined sputtering target may be substantiallytubular.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations. As used herein, the term“cold spray” refers to techniques in which one or more powders arespray-deposited without melting during spraying, e.g., cold spray,kinetic spray, and the like. The sprayed powders may be heated prior toand during deposition, but only to temperatures below their meltingpoints. As used herein, the terms “approximately” and “substantially”mean±10%, and in some embodiments, ±5%. The term “consists essentiallyof” means excluding other materials that contribute to function, unlessotherwise defined herein. Nonetheless, such other materials may bepresent, collectively or individually, in trace amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIGS. 1A and 1B are schematic plan views of joined sputtering targets inaccordance with various embodiments of the invention;

FIGS. 2A-2F are schematic cross-sections of two sputtering-target tilesbeing joined via utilization of a releasable rod and spray deposition inaccordance with various embodiments of the invention;

FIGS. 3A-3F are schematic cross-sections of two sputtering-target tilesbeing joined via utilization of a gap-filling weld bead and spraydeposition in accordance with various embodiments of the invention;

FIGS. 4A-4E are schematic cross-sections of two interlockingsputtering-target tiles being joined via welding and spray deposition inaccordance with various embodiments of the invention;

FIGS. 5A-5E are schematic cross-sections of two overlappingsputtering-target tiles being joined via welding and spray deposition inaccordance with various embodiments of the invention;

FIGS. 6A-6D are schematic cross-sections of two sputtering-target tilesbeing joined via welding in accordance with various embodiments of theinvention;

FIGS. 6E and 6F are cross-sectional micrographs of sputtering targettiles joined in accordance with various embodiments of the invention;

FIGS. 7A-7C are schematic cross-sections of two abuttingsputtering-target tiles being joined via spray deposition in accordancewith various embodiments of the invention;

FIG. 7D is a schematic cross-section of a joined sputtering targetformed of two interlocking sputtering-target tiles joined by theinterlocking joint and by spray deposition in accordance with variousembodiments of the invention;

FIG. 8A is a cross-sectional micrograph of the microstructure of ajoined sputtering target at the sputtering-target tile/sprayed materialinterface prior to annealing in accordance with various embodiments ofthe invention;

FIG. 8B is a cross-sectional micrograph of the microstructure of ajoined sputtering target at the sputtering-target tile/sprayed materialinterface after annealing in accordance with various embodiments of theinvention;

FIG. 9A is a schematic cross-section of two beveled sputtering-targettiles prior to being joined in accordance with various embodiments ofthe invention;

FIG. 9B is a schematic cross-section of two beveled sputtering-targettiles after being joined by spray deposition in accordance with variousembodiments of the invention; and

FIGS. 10A-10D are schematic cross-sections of sputtering-target tileshaving different reentrant bevels in accordance with various embodimentsof the invention.

DETAILED DESCRIPTION

FIGS. 1A and 1B are schematic plan views of joined sputtering targets100 formed by the joining of smaller sputtering-target tiles 110 inaccordance with embodiments of the invention. As shown, the tiles 110are joined via regions 120 that, at least in part, include or consistessentially of one or more spray materials formed by spray deposition(e.g., cold spray, thermal spray, plasma spray, etc.). As shown, thetiles may be substantially rectilinear (FIG. 1A) or tubular (FIG. 1B)and may be joined on one or two sides. In other embodiments the tileshave other shapes (e.g., square) and/or are joined on more than twosides. The tiles may each be of substantially the same size and/orshape, or two or more of the tiles may have different sizes and/orshapes. In various embodiments, regions of the tiles are substantiallyplanar or tubular (e.g., in portions between the regions 120), and thejoined target 100 may be substantially planar or tubular. A joinedtarget 100 may be disposed on a backing plate (not visible in FIG. 1A)or backing tube 130 (portions of which are visible in FIG. 1B) eitherbefore or after formation of the joining regions 120.

The backing plate or tube 130 may include or consist essentially of ametal such as Cu and/or Al, and may have a melting point below that ofthe material of tiles 110 and/or the material of regions 120, and mayeven have a melting point below the temperature that the sprayedmaterial constituting regions 120 reaches during spray deposition (e.g.,in cases where the backing plate or tube is attached to the joinedtarget 100 after formation of regions 120). In some embodiments of theinvention, particularly those in which the joined target is tubular, thebacking plate or tube 130 may include or consist essentially of a metalsuch as stainless steel and/or Ti. The tiles 110 typically include orconsist essentially of one or more metallic materials, e.g., Ti, Nb, Ta,W, Mo, other refractory metals, or composite materials (alloys ormixtures) such as Mo/Ti, W/Ti, Cu/W, etc. The regions 120 preferablyinclude or consist essentially of at least one of the constituentmaterials of tiles 110. For example, the sprayed material in regions 120may include or consist essentially of the same elemental metal as intiles 110, one or more of the constituent metals of a composite tile 110(e.g., a tile 110 may include or consist essentially of Mo/Ti, and theregion 120 may include or consist essentially of Ti), or the sameplurality of constituent metals of a composite tile 110, in the sameconcentration as in tile 110 or in a different mix of concentrations asin tile 110 (e.g., a tile 110 may include or consist essentially of 50%Mo and 50% Ti, and the region 120 may include or consist essentially of40% Mo and 60% Ti). The tiles 110 and regions 120 preferably include orconsist essentially of the same material(s) so that, when the joinedtarget 100 is sputtered, the composition of the material sputtered fromthe target 100 is substantially constant across the dimensions of target100 and as a function of sputtering time and/or lifetime (i.e., amountof utilization) of target 100.

FIGS. 2A-2F schematically depict, in cross-section, various steps of aprocess for forming a joined sputtering target in accordance withvarious embodiments of the present invention. FIGS. 2A-2F (and mostsubsequent figures) depict either substantially planar tiles 110 (i.e.,utilized to fabricate a planar joined target 100) or to portions ofsubstantially tubular tiles 110 (i.e., utilized to fabricate a tubularjoined target 100), which appear planar in cross-section. (Specifically,the cross-section of a tubular tile 110 would include two substantiallyparallel regions, only one of which is shown for each tile 110 in FIGS.2A-2F and many subsequent figures.) As shown in FIG. 2A, a bevel 200 isformed in at least one of the tiles 110, and the tiles 110 arepositioned with a gap 210 at the interface between the tiles 110. Thegap 210 may range from, e.g., approximately 2 mm to approximately 8 mm.As shown, bevels 200 are formed in both tiles 110, but in otherembodiments a bevel (or chamfer) 200 is formed in only one of the tiles110. While the bevels 200 in FIG. 2A are shown as having sloped andstraight sidewalls, other embodiments of the invention feature bevels200 having curved or even arbitrary sidewalls (and/or may be reentrant,as described in more detail below), and the bevels 200 may be asymmetricrelative to the interface between the tiles 110 (i.e., any portion ofthe tiles 110 in close proximity or in contact). The bevels 200 may evenbe asymmetric relative to the horizontal axis (i.e., perpendicular tothe interface between tiles 110) defined by the tiles 110 atapproximately one-half of their thicknesses. Generally, the bevel(s) 200may form any type of recess (i.e., a region depressed relative to thetop surface and/or the bottom surface of at least one of the tiles 110and at least partially defined by bevel(s) 200 of neighboring tiles 110)along an interface between tiles 110 that does not disturb closeproximity or contact between at least a portion of the opposed faces ofthe tiles 110. As shown in FIG. 2A, the bevels 200 may define recessesrelative to both the top and bottom surfaces of tiles 110. While FIG. 2Adepicts the tiles 110 as being entirely separated by gap 210, portionsof the tiles 110 may be in physical contact, and irregularities alongthe edge of at least one of the tiles 110 may at least partially definethe gap 210. In various embodiments, substantially all of a sidewall ofat least one of the tiles 110 may be beveled (i.e., cut at a non-rightangle to the top and/or bottom surface of the tile), and the two tiles110 may be placed in close proximity but not in contact prior to joiningvia spray deposition (as detailed below). In such embodiments thebevel(s) 200 increase the volume of the area to be at least partiallyfilled by spray deposition and/or the surface area of contact betweenthe sprayed material and the tiles 110.

As shown in FIG. 2B, the tiles 110 may be positioned on a supportfixture 220, which may include or consist essentially of any suitablyrigid material (e.g., metal, ceramic, or even wood) and that ispreferably substantially planar. (For tubular tiles 110, the fixture 220may be cylindrical or tubular and disposed within the annular spacedefined by the tiles 110.) Additionally, at least a portion of the gap210 (e.g., along its length perpendicular to the plane of the page ofFIGS. 2A-2F) is substantially filed with a gap-fill material such as arod 230. The rod 230 may have a cross-section that is substantiallycircular or elliptical, as shown in FIG. 2B, or it may have any othercross-sectional shape suitable for filling at least a portion of the gap210. Rod 230 may be substantially solid or hollow, and it preferablyincludes or consists essentially of the material of tiles 110 ormaterial subsequently sprayed thereon (as detailed below), or at leastone constituent material of tiles 110 or such sprayed material. Suchcompositional matching may reduce or substantially eliminate anycontamination due to rod 230 from the final joined target, as the rod230 is typically substantially or completely removed during the processdetailed below. As shown in FIG. 2B, a recess 240 may be at leastpartially defined by the bevels in tiles 110 and a portion of thegap-fill material (here rod 230). The rod 230 may have a diameter oredge length ranging, e.g., from approximately 3 mm to approximately 9mm. The diameter or edge length of the rod 230 may preferably be lessthan one-half of the thickness of the tiles 110 being joined. In someembodiments, the rod 230 is deformable to substantially “seal” the gap210 and thereby substantially prevent the flow of powder particlesduring subsequent spray deposition (as detailed below).

After rod 230 has been positioned to fill at least a portion of the gap210, a material 250 is spray-deposited thereover to partially orsubstantially fill the recess 240. The sprayed material 250 ispreferably deposited by cold spray, and thus includes or consistsessentially of substantially unmelted powder, but in particularinstances may instead be deposited by other spray-deposition methodssuch as plasma spray or other thermal spray techniques (and thus sprayedmaterial 250 may include or consist essentially of substantially meltedpowder). The volume of spray-deposited material 250 present within therecess 240 typically forms a partial joint joining the two tiles 110.The amount of material 250 at the partial joint, enabled by the recess240 at least partially formed by the bevel(s) 200, contributes to thestrength of the joint and thus of the entire joined sputtering targetafter completion. The material 250 preferably includes or consistsessentially of the material of tiles 110, or at least one constituentmaterial of tiles 110 (for tiles 110 that are composites of multipleconstituent materials), as described above in relation to FIGS. 1A and1B.

After spray-deposition of the material 250 to form the partial jointbetween the tiles 110, the rod 230 is removed from the tiles 110 and thematerial 250 by, e.g., mechanical force, grinding, and/or dissolution inan acidic agent. Preferably the entire rod 230 is removed, even if smallportions of the material 250 and/or the tiles 110 are removed along withrod 230. As shown in FIG. 2D, the tiles 110 may then be flipped over andmay be positioned on fixture 220 (not shown) or another suitable fixturefor mechanical support. As shown in FIG. 2E, a recess 260 at leastpartially defined by the bevels 200 and the material 250 is subsequentlyfilled (at least partially), preferably with the same material asmaterial 250, to form the region (or “joint”) 120 joining the tiles 110.As shown, the sprayed material may be deposited to be substantiallycoplanar with the surfaces of the joined tiles 110, thus providing thejoined target 100 with one or more surfaces that are substantiallyplanar. As also shown, at least a portion of the joint 120 may consistessentially of the sprayed material through its entire thickness; asdescribed in more detail below, such a configuration may result in amechanically stronger joint 120. As shown in FIG. 2F, the tiles 110 (oreffectively, the joined target 100) may be attached to a backing plate130 either before or after the sprayed material is deposited within therecess 160 to complete the joint 120.

After formation of the joint 120, the joined target 100 (at leastproximate the joint 120) may be heat treated for stress relief (e.g., toimprove ductility) and/or to provide the joint 120 with a microstructuresubstantially equal to that of the joined tiles 110. For example, fortiles 110 including or consisting essentially of a mixture of multipleconstituents, the microstructure of the tiles 110 may includeinterdiffused regions between regions corresponding to differentconstituents (as described in more detail below with reference to FIGS.8A and 8B; for example, arising from a HIP process for forming the tiles110). After a heat treatment, the joint 120 may feature suchinterdiffused regions, which may have approximately the same size ofsuch regions in the tiles 110 prior to joining. In some embodiments ofthe invention, the heat treatment may be performed under vacuum, at atemperature between approximately 700° C. and approximately 900° C., andfor a time between approximately 1 hour and approximately 16 hours.

In addition, the heat treatment may relieve residual stresses from thespray-deposition process. For example, in many cases, sprayed materialmelted during spraying tends to have tensile residual stress, whilesprayed material that is not melted during spraying tends to havecompressive residual stress. (For example, cold-sprayed Ta may haveresidual compressive stress of between 30 and 50,000 psi.) Such residualstresses may result in non-uniform sputtering rates from the targetincorporating the sprayed material. In conventional (i.e., notincorporating sprayed material) targets, residual machining stressesfrequently necessitate a costly burn-in period (i.e., sputtering away ofthe stressed surface layer) prior to sputtering with new targets.Embodiments of the present invention described herein facilitate themanufacture of joined sputtering targets and subsequent heat treatmentprior to the target being joined to a backing plate. (The backing plateand the joining compound, e.g., In solder, typically have lower meltingpoints and thus may not be able to withstand a heat treatment adequateto reduce or substantially eliminate residual stress from the target.)In this manner, the need for a burn-in period prior to sputtering fromthe joined target is reduced or substantially eliminated.

FIGS. 3A-3F depict another process for forming a joined sputteringtarget 100 utilizing a gap-fill material between sputtering-target tiles110 in accordance with embodiments of the present invention. Asdescribed above in relation to FIG. 2A, the tiles 100 have one or morebevels 200 and are positioned with gap 210 at the interface between thetiles 110 (which may result, as discussed above, from portions of thetiles 110 being in contact or close proximity at the interface). Asshown in FIG. 3B, in various embodiments of the invention, at least aportion of the gap 210 is subsequently filled with a gap-fill materialthat includes or consists essentially of a weld bead 300 disposed in arecess 310 at least partially defined by the bevels 200. The weld bead300 may be formed by, e.g., tungsten inert gas (TIG) welding (utilizingan inert cover gas such as helium or argon), and may be formed with orwithout the use of a filler wire or rod (which preferably includes orconsists essentially of the material of tiles 110 or at least oneconstituent material thereof). The weld bead 300 thus includes orconsists essentially of portions of the tiles 110 and/or the fillermaterial. The weld bead 300 may be a substantially continuous bead alongthe entire interface between the tiles 110 or may be a series of spotwelds along the interface. In preferred embodiments in which material issubsequently deposited by cold spray (as detailed below), the weld bead300 is a substantially continuous bead along the entire interfacebetween the tiles 110 that substantially seals the gap 210. As shown inFIG. 3B, formation of the weld bead 300 may alter the microstructure ofone or both tiles 110 near the weld bead 300 (due to, e.g., the elevatedwelding temperature), forming altered regions 320. Region 320 typicallyincludes or consists essentially of a heat-affected zone (HAZ), whichmay be characterized by substantial grain growth compared to regions ofthe tiles 110 outside of the HAZ. The grain growth may result in thesweeping of impurities to the grain boundaries and significantembrittlement of the HAZ for materials such as Mo and its alloys.Additionally, for composite materials such as MoTi, the HAZ may featureincreased porosity (compared to regions of the tiles 110 outside of theHAZ) due to gas evolution due to local melting of one or more of theconstituent materials (e.g., melting of Ti but not of Mo).

After formation of the weld bead 300, the remainder of recess 310 ispartially or substantially filled via spray-deposition of the material250, as shown in FIG. 3C. Afterwards, because the weld bead 300typically has a different microstructure that that of the bulk of thetiles 110, the weld bead 300 is removed from the tiles 110 and thematerial 250, as shown in FIG. 3D. The removal may be performed by,e.g., mechanical grinding and/or chemical (e.g., acid) treatment. Asshown, regions 320 are preferably also removed along with the weld bead300, forming a recess 330 (defined at least in part by bevels 200 andthe surfaces of tiles 110 revealed during removal of weld bead 300and/or regions 320) shown in FIG. 3D. Such removal may also removeportions of the original material 250 deposited in recess 310 and/oradditional portions of the tiles 110. Additional material 250 issubsequently spray-deposited within the recess 330 to complete formationof the joint 120, as shown in FIG. 3E. As shown, the sprayed materialmay be deposited to be substantially coplanar with the surfaces of thejoined tiles 110, thus providing the joined target 100 with one or moresurfaces that are substantially planar. As also shown, at least aportion of the joint 120 may consist essentially of the sprayed materialthrough its entire thickness; as described in more detail below, such aconfiguration may result in a mechanically stronger joint 120. As shownin FIG. 3F, the tiles 110 (or effectively, the joined target 100) may beattached to a backing plate 130 either before or after the sprayedmaterial is deposited within the recess 330 to complete the joint 120.After formation of the joint 120, the joined target 100 (at leastproximate the joint 120) may be heat treated, for example as describedabove with reference to FIGS. 2A-2F.

FIGS. 4A-4E depict a process for forming a joined sputtering target 100utilizing sprayed material and an interlocking joint betweensputtering-target tiles 110 in accordance with embodiments of thepresent invention. Specifically, the tiles 110 may be machined withcomplementary and/or interlocking features 400 that facilitate thejoining of the tiles 110 and improve the strength of the joint 120 afterspray deposition. As shown in FIG. 4B, the interlocking features 400 arejoined to form a mechanical joint 410 (that may be, as detailed below,supplemented with spray-deposited material). While FIGS. 4A-4E depict atongue-in-groove joint, other joints (including, e.g., dovetail joints,rabbet joints, finger joints, spline joints, etc.) may be utilized inconjunction with or instead of a tongue-in-groove joint. Furthermore,joined sputtering targets 100 may utilize different types of joints 410to join different pairs of tiles 110. Generally, the interface betweentwo tiles 110 may have one or more bevels 200, an interlocking feature(or “interlock”) 400, or both. The interlock 400 may have any geometrythat varies the contact interface from a straight interface in order toincrease the contact surface area and/or provide mechanical linkagebetween the tiles 110. Before the tiles 110 are physically joined (i.e.,before they are placed in direct contact with each other) to formmechanical joint 410, one or more portions of the surfaces that willmeet in the locking joint 410 may be coated with a spray-depositedcoating. The coating may be sprayed on all or portions of such surfaceson only one of the tiles 110 or on both of them. Thus, in accordancewith various embodiments, two discrete sputtering-target tiles 100including or consisting essentially of the sputtering material aredisposed proximate each other, thereby forming an interface between thetiles that contains an interlocking joint 410.

As shown in FIG. 4C, the mechanical joint 410 may preferably bestrengthened and/or sealed together via use of welding, e.g., resistanceseam welding. As shown, electrodes 420 are disposed on either side ofmechanical joint 410 and, depending on the length of the joint 410(i.e., out of the plane of the page), translated laterally along thejoint 410. Mechanical force is generally applied to the mechanical joint410 by the electrodes 420, and a large current is applied between thetwo electrodes 420. The heat resulting from the electrical resistance ofthe joint 410 welds the interlocks 400 together to strengthen the joint410. Depending on the materials of tiles 110, a portion thereof withinthe joint 410 may even melt during the welding process. For example, fortiles 110 that include multiple constituent materials, one or more ofthe lower-melting-point constituents may melt during the welding tostrengthen the joint 410 while one or more other constituents (i.e.,having higher melting points) may remain substantially unmelted duringthe welding. In a specific example, for tiles 110 formed of Mo/Ti, theTi may melt during the welding while the Mo phase remains unmelted. Inpreferred embodiments of the present invention, such melting is limited,and most of the bonding between the tiles 110 occurs due to solid-statediffusion between the tiles 110.

As shown in FIG. 4D, the mechanical joint 410 between the tiles 110 maybe subsequently supplemented with a layer of spray-deposited material250 to form joint 120 (which includes or consists essentially of themechanical joint 410 and the layer of sprayed material 250). Thetongue-in-groove joint (or alternative joint, as detailed above) mayhelp prevent the propagation of defects through the subsequently sprayedlayer of material 250. For example, a simple butt joint between the twotiles to be joined may result in a small gap or other discontinuitybetween the tiles at some point along the interface therebetween, andsuch a gap may propagate through the subsequently sprayed layer,weakening the sprayed joint and the final joined target. Accordingly,the tiles are desirably substantially in contact along the interface; by“substantially in contact” is meant that the interface is sufficientlyfree of gaps or discontinuities to avoid their perceptible orperformance-affecting propagation through the sprayed layer of material250. The welding described above with respect to FIG. 4C may be repeatedafter deposition of material 250, for example to enhance adhesionbetween the sprayed material 250 and the tiles 110. As shown in FIG. 4E,the tiles 110 (or effectively, the joined target 100) may be attached toa backing plate 130 either before or after the sprayed material 250 isdeposited to complete the joint 120. After formation of the joint 120,the joined target 100 (at least proximate the joint 120) may be heattreated, for example as described above with reference to FIGS. 2A-2F.

FIGS. 5A-5E depict a process for forming a joined sputtering target 100similar to that depicted in FIGS. 4A-4E but utilizing overlappingsputtering-target tiles 110 in accordance with embodiments of thepresent invention. Specifically, the bevels 200 of tiles 110 may bemachined such that a portion of one tile 110 overlaps a portion of theother tile 110 when the tiles are brought into proximity or substantialcontact. This overlap feature, similar to mechanical joint 410 describedabove, facilitates the joining of the tiles 110 and improves thestrength of the joint 120 after spray deposition. As shown in FIG. 5B,the tiles 110 are brought into close proximity or substantial contact,forming an overlapping region 500 (that may be, as detailed below,supplemented with spray-deposited material). Joined sputtering targets100 may utilize different types of overlapping regions 500 betweendifferent pairs of tiles 110. Before the tiles 110 are placed in directcontact with each other to form overlapping region 500, one or moreportions of the surfaces that will meet in the overlapping region 500may be coated with a spray-deposited coating. The coating may be sprayedon all or portions of such surfaces on only one of the tiles 110 or onboth of them.

As shown in FIG. 5C, the overlapping region 500 may preferably bestrengthened and/or sealed together via use of welding, e.g., resistanceseam welding. As shown, electrodes 420 are disposed on either side ofoverlapping region 500 and, depending on the length of the overlappingregion 500 (i.e., out of the plane of the page), translated laterallyalong the overlapping region 500. Mechanical force is generally appliedto the overlapping region 500 by the electrodes 420, and a large currentis applied between the two electrodes 420. The heat resulting from theelectrical resistance of the overlapping region 500 welds tiles 110together to strengthen the overlapping region 500. Depending on thematerials of tiles 110, a portion thereof within the overlapping region500 may even melt during the welding process. For example, for tiles 110that include multiple constituent materials, one or more of thelower-melting-point constituents may melt during the welding tostrengthen the overlapping region 500 while one or more otherconstituents (i.e., having higher melting points) may remainsubstantially unmelted during the welding. In a specific example, fortiles 110 formed of Mo/Ti, the Ti may melt during the welding while theMo phase remains unmelted.

As shown in FIG. 5D, the overlapping region 500 between the tiles 110may be subsequently supplemented with a layer of spray-depositedmaterial 250 to form joint 120 (which includes or consists essentiallyof the overlapping region 500 and the layer of sprayed material 250).The overlapping region 500 (where the tiles 110 are substantially incontact) may help prevent the propagation of defects through thesubsequently sprayed layer of material 250, as it may eliminate smallgaps or discontinuities between the tiles 110 that may propagate throughthe subsequently sprayed layer, weakening the sprayed joint and thefinal joined target 100. As shown in FIG. 5E, the tiles 110 (oreffectively, the joined target 100) may be attached to a backing plate130 either before or after the sprayed material 250 is deposited tocomplete the joint 120. After formation of the joint 120, the joinedtarget 100 (at least proximate the joint 120) may be heat treated, forexample as described above with reference to FIGS. 2A-2F.

In some embodiments of the present invention, particularly thoseutilizing thinner sputtering-target tiles 110, the tiles 110 may bejoined to form a joined target 100 utilizing welding (e.g., resistanceseam welding) without material spray-deposited over the resulting weldedjoint. As shown in FIG. 6A, the tiles 110 may be provided withcomplementary bevels 200 such that, as shown in FIG. 6B, the tiles 110may be fit together substantially gaplessly (and preferably withoutrecesses on the top and bottom surfaces on the resulting joined tile).Before the tiles 110 are placed in direct contact with each other, oneor more portions of the bevels 200 may be coated with a spray-depositedcoating (e.g., including or consisting essentially of one or more, oreven all, of the constituent materials of tiles 110, or even of the samematerial as that of tiles 110). The coating may be sprayed on all orportions of bevels 200 on only one of the tiles 110 or on both of them.

As shown in FIG. 6C, the interface between the tiles 110 is thenstrengthened and/or sealed together via use of welding, e.g., resistanceseam welding. As shown, electrodes 420 are disposed on either side ofthe interface and, depending on the length of the interface (i.e., outof the plane of the page), translated laterally along the interface.Mechanical force is generally applied to the interface by the electrodes420, and a large current is applied between the two electrodes 420. Theheat resulting from the electrical resistance of the tiles 110 weldstiles 110 together to strengthen the bond between the tiles 110.Depending on the materials of tiles 110, a portion thereof may even meltduring the welding process. For example, for tiles 110 that includemultiple constituent materials, one or more of the lower-melting-pointconstituents may melt during the welding to strengthen the joint whileone or more other constituents (i.e., having higher melting points) mayremain substantially unmelted during the welding. In a specific example,for tiles 110 formed of Mo/Ti, the Ti may melt during the welding whilethe Mo phase remains unmelted. As shown in FIG. 6D, the tiles 110 (oreffectively, the joined target 100) may be attached to a backing plate130 after the welding process that forms joint 600. After formation ofthe joint 600, the joined target 100 (at least proximate the joint 600)may be heat treated, for example as described above with reference toFIGS. 2A-2F.

In some embodiments of the present invention, the above-describedwelding technique joins composite tiles 110 together via preferentialbonding (via, e.g., at least partial melting and/or solid-statediffusion) of only one of (or less than all of) the constituents of thetiles, e.g., the constituent(s) having lower individual meltingpoint(s). FIG. 6E is a micrograph of two Mo/Ti composite tiles joined insuch a manner, in which preferential bonding was achieved via adjustmentof the power density utilized in the welding process. As shown, Tiregions in the two tiles 110 are preferentially bonded to other Tiregions and to Mo regions across a bonding interface 610, but Mo regionsof the two tiles 110 that abut at interface 610 have not bonded (atleast not completely). The tiles 110 shown in FIG. 6E were approximately9 mm thick, and the resulting bonding was successful across the fullthickness. Closure pressure of the welding electrodes was approximately55 MPa and the weld current density was 50 kA/m². Tiles 110 havinglarger thicknesses (e.g., up to 20 mm, or even thicker) may be joinedwith the techniques described herein by, e.g., increasing the weldpressure and/or the weld power density. The welding may be performed atspeeds of, e.g., 10-16 cm/min, or even faster.

As shown in FIG. 6E, the two tiles 110 have been bonded together whileretaining the microstructure of the tiles 110 in the vicinity of thebonding interface 610 without formation of a HAZ and without theabove-described concomitant properties of a HAZ. Moreover, tiles 110joined via this technique have sufficient bonding strength at interface610 such that the interface 610 is not a failure point when stress isapplied to the joined target. FIG. 6F depicts a joined sputtering targetfabricated via seam welding of two tiles 110 after tensile stresstesting to fracture. As shown, the fracture 620 does not correspond toor follow the bonding interface 610 (shown schematically by the dashedline). In addition, as in FIG. 6E, the microstructure along theinterface 610 is substantially identical to that of the two tiles 110away from interface 610, demonstrating that the joining process does notdisrupt the microstructure of the tiles 110.

FIGS. 7A-7D illustrate another embodiment of the present invention inwhich sputtering-target tiles 110 are brought into substantial contactand a joint 120 between the tiles 110 is formed via spray deposition. Asshown, one or both of the tiles 110 has a bevel 200 that, when the tiles110 are brought into substantial contact, defines a recess 700 above theinterface 710 between the tiles 110. As shown in FIG. 7D, the interface710 may include or consist essentially of a mechanical joint 410 (asdescribed above) rather than a butt joint between the tiles 110. Theinterface 710 is preferably substantially free of gaps, as such gaps mayresult in cracks or other points of weakness propagating throughmaterial spray-deposited above the interface 710. As shown in FIGS. 7Cand 7D, after the tiles 110 are brought together and are substantiallyin contact, material 250 is spray-deposited within recess 700 to formjoint 120. The material 250 is preferably sprayed to form a top surfacesubstantially coplanar with the top surfaces of the tiles 110, such thatthe joined tile 100 has a substantially planar top surface. As alsoshown in FIGS. 7C and 7D, the tiles 110 (or effectively, the joinedtarget 100) may be attached to a backing plate 130 either before orafter the sprayed material 250 is deposited to complete the joint 120.After formation of the joint 120, the joined target 100 (at leastproximate the joint 120) may be heat treated, for example as describedabove with reference to FIGS. 2A-2F.

Various embodiments of the present invention incorporate annealing stepsto strengthen any or all of (i) the original material matrix of thetiles 110, (ii) the spray-deposited joint 120, and (iii) the bondingregion between the original tile matrix and the sprayed layer (i.e., thetensile strength across the interface between the original tile and thesprayed layer). The table below shows the increase in tensile strengthin all three regions for two different anneal conditions, a 16-houranneal at 700° C. and a one-hour anneal at 900° C. In these joinedtargets, which are formed of MoTi, the original tile matrix was formedby HIP and the sprayed layer was formed by cold spray.

Tile Matrix Sprayed Layer Bonding Region (psi) (psi) (psi) No anneal64,958 28,600 1,297 700° C., 16 hours 108,667 74,273 7,881 900° C., 1hour 94,793 57,364 6,445

As shown in the table, both annealing conditions significantly increasethe tensile strength of the joined target in all three regions. FIGS. 8Aand 8B depict one contributor to the increased strength in the annealedtargets. FIG. 8A is a cross-sectional micrograph of a spray joined MoTitile in accordance with various embodiments of the invention beforeannealing, in which the original tile 110 matrix was formed by HIP andthe sprayed layer 250 was formed by cold spray. As shown in FIG. 8A andas the above table indicates, the matrix of the original tile 110 has ahigher initial tensile strength at least in part because the matrixincludes not only discrete Mo and Ti phases (the light and dark areas),but also an interdiffused region 800 (indicated in gray) therebetween.In contrast, the sprayed layer 250 consists essentially of the pure Moand Ti phases without any interdiffusion (likely due to the reducedtemperature of the cold-spray process).

FIG. 8B is a cross-sectional micrograph of the same sample afterannealing, where the original material matrix of the tile 110, the layerof spray-deposited material 250, and the bonding region between theoriginal tile 110 matrix and the sprayed layer 250 all exhibit highertensile strength (as shown in the above table). As shown in FIG. 8B, theannealing step has increased the size of the interdiffused area 800 inthe original tile matrix and resulted in formation of interdiffusedareas 810 in the spray-deposited layer 250. Furthermore, interdiffusedmaterial is evident at the bonding interface between the two regions,demonstrating that the anneal has resulted in diffusion bonding betweenthe original tile 110 matrix and the sprayed layer 250, thus resultingin enhanced mechanical strength of the joined target 100. Theinterdiffused areas 800, 810 include or consist essentially of two ormore (or even all) of the constituent materials of the tiles 110, whileother areas of the tiles 100 and/or the sprayed material 250, at themicroscale, include or consist only fewer (or even only one) of theconstituents, as shown in FIGS. 8A and 8B. Various embodiments of thepresent invention incorporate a high-temperature annealing step afterspray-deposition of the joining layer(s) 120 between the tiles 110. Theannealing step is preferably of sufficient temperature and time toresult in diffusion bonding between the tile(s) 110 and the material 250of the sprayed joint 120. For example, the annealing step may beperformed for a time between approximately ½ hour and approximately 20hours and at a temperature between approximately 480° C. andapproximately 1425° C., or at a temperature between approximately 1100°C. and approximately 1425° C. (i.e., higher than the melting point ofconventional backing plates and soldering materials utilized to joinsputtering targets to backing plates, e.g., In solder). In embodimentsin which the tiles 110 are composites of multiple constituent materials,a thin layer of one or more (but not all) of the constituent materials(e.g., Ti for a Mo/Ti tile 110) may be spray-deposited prior to thespraying of the remaining material 250 (which may include or consistessentially of the material of the tiles 110, e.g., Mo/Ti). This thinlayer may further improve bonding and interdiffusion across the joint120. For example, for Mo/Ti tiles 110, a thin layer of Ti maysubstantially prevent Mo-to-Mo contact across the interface between thetile 110 and the sprayed material 250, where Mo self-contact may havelittle or no adhesive strength. The thickness of the thin layer may be,e.g., approximately 50 μm to approximately 100 μm, and/or the thicknessmay be approximately the same or slightly (e.g., 5-20%) larger than theaverage diameter of particles of one or more of the constituents in thelayer. (For example, for a thin layer of Ti for a Mo/Ti tile 110, thethickness of the thin layer may be approximately the same or slightlylarger than the average diameter of the Mo particles to substantiallyprevent self-contact thereof.)

As mentioned above, the bevels 200 formed in tiles 110 to be joined mayhave any of a variety of shapes and make a variety of different angleswith respect to the substantially planar top and/or bottom surfaces.(For tubular targets, the top and bottom surfaces are generally planarwhen viewed in cross-section, even though the surfaces themselves havecurvature, as discussed above.) FIG. 9A depicts two tiles 110 to bejoined in accordance with embodiments of the present invention eachhaving a bevel 200 that is substantially planar and forms a bevel angleA with respect to the normal to the top and bottom surfaces. Tensilestrength measurements were performed on three samples each havingdifferent angles A, where at each joint 120 each tile 110 had a bevel ofangle A, and thus the entire included angle at the joint was 2A, asshown in FIG. 9B. The samples were tested utilizing the ASTM three-pointbending test where loading was applied to the center of the joint 120.The table below presents the fracture stress for each sample, as well asthe location of the crack formation at failure (in the matrix of theoriginal tile 110, within the sprayed layer of material 250, and/or atthe bonding interface therebetween).

Crack Crack Crack Bevel Fracture Std. in in in Angle A Stress Dev. TileSprayed Interfacial (degrees) Anneal (psi) (psi) Matrix Layer Region 45None 1900 1550 X 45 700° C. 11,250 15,700 X 16 hours 45 900° C. 14,44013,360 X 1 hour 52.5 None 3580 1382 X 52.5 700° C. 4480 2743 X 16 hours52.5 900° C. 1710 1205 X 1 hour 60 None 13,010 4670 X 60 700° C. 28,4401920 X X 16 hours 60 900° C. 32,860 4210 X X 1 hour

As shown in the above table, generally the fracture strength of thejoined target 100 increases with increasing bevel angle A. Moreover,failure was more likely to occur within the stronger sprayed joint 120than only within the interfacial region as the bevel angle A increases.In these samples, the spray-deposited joint 120 was sprayed normal tothe top surface of the target 100 (rather than to the surface of thebevel 200 itself); thus, fracture strength of the joint 120 increases asthe spray direction approaches perpendicular to the surface of the bevel200. Therefore, in various embodiments of the invention, at least aportion (and preferably an initial portion) of the spray-deposited layerjoining the tiles is sprayed substantially perpendicular to the surface(or at least a portion thereof) of the bevel 200 formed in the tile 110.For example, a first portion of the sprayed layer 120 may be depositedin a direction substantially perpendicular to the surface of the bevel200, and a second portion may substantially fill the remaining recessand be sprayed substantially perpendicular to the top surfaces of thetiles 110 being joined. The first portion may have a thickness of, e.g.,between 1 μm and 10 μm, or even between 10 μm and 100 μm, or eventhicker than 100 μm. In various embodiments of the invention, the firstand second portions of the sprayed layer 120 may be distinguished viaexamination of the microstructure of the sprayed powder. For example,when powder is deposited via cold spray, the powder particles tend toflatten on impact (having slowed from supersonic velocity) with thesubstrate, and the particles are flattened along the spraying direction.(That is, an initially spherical particle will be flattened such thatits surfaces approximately parallel to the spraying direction are closertogether than its other surfaces.

In another embodiment, the bevel 200 formed in a tile 110 to be joinedmay even have a slight concavity and may thus be more parallel to thetop and/or bottom surfaces of the tile 110 in the proximity of thejoining edge of the tile 110. In such embodiments typical spraydeposition angles approximately perpendicular to the tile 110 topsurface will be more perpendicular to the surface of the bevel 200 inthe center of the joint 120 (i.e., the region of the joint 120 thattends to have the least mechanical strength), thereby strengthening thejoint 120.

Various embodiments of the present invention utilize bevels 200 havingreentrant surfaces to facilitate formation of stronger spray-depositedjoints 120. FIGS. 10A-10D depict exemplary reentrant bevels inaccordance with embodiments of the present invention. As utilized hereina “reentrant surface” is one through which a straight line (illustratedin FIGS. 10A-10D as dashed lines) may be drawn such that it enters,exits and re-enters the surface at least once, or even twice or more. Ingeneral, the number of exit and re-entry points is one of the parametersthat may be varied to optimize the reentrant surface of the bevel(s) 200for strength of the joint 120. Reentrant surfaces may be composed of twoor more generally straight segments and may feature one or moreinflection points indicating changes in slope. Three-point fracturestrength measurements were performed on two different samples eachhaving the reentrant bevel surface illustrated in FIG. 10A, butemploying different radii R₁, R₂ on the curved sections. Specimen 1 hada 4 mm radius R₂ of the concave-down surface and a 1 mm radius R₁ of theconcave-up surface. In specimen 2, both radii were 2.5 mm. The sampleswere tested utilizing the ASTM three-point bending test where loadingwas applied to the center of a spray-deposited joint 120 between thetiles 110 (as shown, e.g., in FIG. 9B for tiles 110 without reentrantbevels 200). The table below presents the fracture stress for eachsample, as well as the location of the crack at failure (in the matrixof the tile 100, within the sprayed layer 120, and/or at the bondinginterface therebetween).

Crack Crack Crack Fracture Std. in in in Sample Stress Dev. Tile SprayedBonding No. Anneal (psi) (psi) Matrix Layer Region 1 None 11,800 771 X 1700° C. 38,910 3875 X X 16 hours 1 900° C. 38,860 13,113 X 1 hour 2 None13,230 4547 X 2 700° C. 48,170 9545 X 16 hours 2 900° C. 51,080 2006 X 1hour

As shown, the use of reentrant bevel surfaces not only results ingenerally stronger joints, but also shifts the failure location from theweaker interfacial bonding region to within the bulk of the sprayedlayer 120 itself and sometimes even into the matrix of one of the tiles110. Thus, the reentrant surface 200, at least in some embodiments,shifts the region of peak stress of the joined tile 100 away from theweakest part of the joint to a region of more mechanical strength.

Tiled sputtering targets 100 with spray-deposited joints 120, asdescribed herein, do not only meet the larger size requirements of manysputtering applications, but also facilitate greater materialutilization during sputtering. In magnetron sputtering with a set ofindividual tiles, the magnetron generally needs to provide a fixedelectric field for each tile. Because of the shape of the field, theerosion pattern takes on the form of a race track in the plate, wherethe edges and the center of the tile are sputtered little if at all,resulting in the utilization of only about 30% of the target mass. Onthe other hand, a large tiled sputtering target, as provided by variousembodiments of the present invention, facilitates use of a sweepingmagnetron that causes a more uniform, larger erosion pattern (akin tothe shape of an empty bath tub), as a result of which up to about 60% ofthe target may be sputtered.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is:
 1. A joined sputtering target comprising: twosputtering-target tiles (A) each comprising a sputtering material, and(B) at least partially joined together via a mechanical joint at aninterface therebetween, the mechanical joint comprising portions of thesputtering-target tiles either (i) overlapping each other or (ii)overlapping and interlocking each other at the interface; and a regionof metal powder disposed over the interface and in contact with the twosputtering-target tiles.
 2. The joined sputtering target of claim 1,wherein the sputtering material comprises a mixture or alloy of at leasttwo constituent materials.
 3. The joined sputtering target of claim 2,wherein the at least two constituent materials comprise Mo and Ti. 4.The joined sputtering target of claim 2, wherein the metal powdercomprises at least one of the constituent materials.
 5. The joinedsputtering target of claim 1, wherein the metal powder comprises thesputtering material.
 6. The joined sputtering target of claim 1, whereinthe metal powder consists essentially of the sputtering material.
 7. Thejoined sputtering target of claim 1, wherein the two sputtering-targettiles each consists essentially of the sputtering material.
 8. Thejoined sputtering target of claim 7, wherein the metal powder consistsessentially of the sputtering material.
 9. The joined sputtering targetof claim 1, wherein the mechanical joint comprises an interlockingjoint, the interlocking joint comprising a tongue-in-groove joint, adovetail joint, a rabbet joint, a finger joint, or a spline joint. 10.The joined sputtering target of claim 1, wherein at least a portion ofeach of the two sputtering-target tiles is substantially planar.
 11. Thejoined sputtering target of claim 1, wherein at least a portion of eachof the two sputtering-target tiles is substantially tubular.
 12. Thejoined sputtering target of claim 1, wherein at least a portion of themetal powder is disposed within a recess defined by at least one of thesputtering-target tiles.
 13. The joined sputtering target of claim 12,wherein the recess is defined by a beveled surface of at least one ofthe two sputtering-target tiles.
 14. The joined sputtering target ofclaim 13, wherein the beveled surface is reentrant.
 15. The joinedsputtering target of claim 13, wherein at least a portion of the beveledsurface is substantially planar and forms an angle of greater than 45°with respect to a normal to a top surface of the joined sputteringtarget.
 16. The joined sputtering target of claim 15, wherein the angleis selected from the range of 45° to 60°.
 17. The joined sputteringtarget of claim 1, wherein the metal powder is substantially unmelted.18. The joined sputtering target of claim 1, further comprising abacking plate on which the two sputtering-target tiles are disposed. 19.The joined sputtering target of claim 1, wherein the mechanical jointcomprises portions of the sputtering-target tiles overlapping each otherat the interface.
 20. The joined sputtering target of claim 1, whereinthe mechanical joint comprises portions of the sputtering-target tilesoverlapping and interlocking each other at the interface.
 21. The joinedsputtering target of claim 1, wherein the two sputtering-target tilesare welded together at the interface.
 22. The joined sputtering targetof claim 1, wherein the sputtering material comprises at least one ofmolybdenum, titanium, copper, tungsten, niobium, or tantalum.